Abstract Intellectual disability (ID) is differently yet validly described by different professions. Legal professionals find it most useful to consider ID as a disability rather than a disorder. Because the law regulates the actions of individuals in a society and the actions of society on an individual, the law's concern in dealing with a person with ID is almost always with that person's functional abilities and limitations in society. This concern is reflected in various aspects of criminal and civil law, although the methods of assessing those functional abilities and limitations have changed considerably over time. The law has not always been wise or humane in its treatment of people with ID, but its focus on functional abilities and limitations allows us to assist people with ID to use their abilities and participate in society to their fullest potential.